Battery Pack

ABSTRACT

A battery pack includes a housing and electrochemical cells disposed in the housing. The housing includes a container and a lid that closes an open end of the container. The container has a base, an outer wall the surrounds the base, and a first and a second inner wall disposed inside the outer wall. The first inner wall extends between, and is fixed to, a first portion and a third portion of the outer wall, and is spaced apart from a second portion and a fourth portion of the outer wall. The second inner wall extends between the first portion and the third portion, and is disposed between the first inner wall and the fourth portion. The second inner wall is movable relative to the outer wall such that spacing of the second inner wall from the first inner wall can be changed.

BACKGROUND

1. Field of the Invention

The present invention relates to a battery pack for storage ofelectrochemical cells, including a battery pack housing having passivecooling features as well as features that minimize outer wall stress dueto electrochemical cell growth.

2. Description of the Related Art

Battery packs provide power for various technologies ranging fromportable electronics to renewable power systems and environmentallyfriendly vehicles. For example, hybrid electric vehicles (HEV) use abattery pack and an electric motor in conjunction with a combustionengine to increase fuel efficiency. Battery packs are formed of aplurality of battery modules, where each battery module includes severalelectrochemical cells. The cells are arranged in stacks and areelectrically connected in series or in parallel. Likewise, the batterymodules within a battery pack are electrically connected in series or inparallel.

Some battery packs used with conventional hybrid electric vehicles aredesigned to provide a relatively high voltage, for example 400 volts(V). To achieve the high voltage, battery packs are relatively large andinclude hundreds of electrochemical cells. Moreover, to accommodate thehigh voltage, the components in the electrical system are relativelyexpensive and subject to high voltage protection requirements. It isdesirable to form a battery pack which has fewer and less expensivecomponents.

SUMMARY

In some aspects, a battery pack housing is configured to receive aplurality of electrochemical cells. The battery pack housing includes acontainer, and the container includes a base, an outer wall, a firstinner wall and a second inner wall. The base includes an inner surface,an outer surface opposed to the inner surface, and a peripheral edgethat joins the inner surface to the outer surface. The outer wallsurrounds the peripheral edge and protrudes from the base in a directionthat is normal to the inner surface of the base. The outer wall includesa first portion, a second portion adjoining the first portion, a thirdportion adjoining the second portion and opposed to the first portion,and a fourth portion opposed to the second portion. The first inner wallextends between the first portion and the third portion, and the firstinner wall is fixed to each of the first portion and the third portion.The second inner wall extends between the first portion and the thirdportion, and is disposed between the first inner wall and the fourthportion. The second inner wall is movable relative to the outer wallsuch that a spacing of the second inner wall from the first inner wallcan be changed.

The battery pack housing may include one or more of the followingfeatures: The first inner wall is spaced apart from the second portionand the fourth portion, whereby a gap exists between the first innerwall and the second portion. Each of the first inner wall and the secondinner wall is hollow and includes opposed inner and outer surfaces andribs that extend between the opposed inner and outer surfaces, the ribsdefining vacancies within each of the first inner wall and the secondinner wall. A spacer is disposed between the second inner wall and thefourth portion. The second inner wall has an inner surface that isparallel to and faces the second portion, and an outer surface thatfaces the fourth portion, and at least a portion of the outer surface ofthe second inner wall is not parallel to the fourth portion. A portionof an outer surface of the outer wall is formed having outwardlyprotruding cooling ribs. The battery pack housing is formed of anon-electrically conductive material. The outer wall is formed of afirst element, a second element formed separately from, and detachablyconnected to, the first element, and a latching member. The firstelement includes the first portion, the second portion and the thirdportion arranged in a U-shape. An inner surface of the first elementincludes first surface features configured to receive the latchingmember. The second element includes the fourth portion, and an innersurface of the second element includes second surface featuresconfigured to receive the latching member and cooperate with firstsurface features to detachably connect the first element to the secondelement. The second element includes the second inner wall, and thesecond inner wall is parallel to and spaced apart from the fourthportion via a spacer. The latching member is a pin, the first surfacefeatures include a first through opening and the second surface featuresinclude a second through opening, and the pin extends through both thefirst through opening and the second through opening. The second throughopening is aligned with the first through opening along an axis normalto the inner surface of the base.

In some aspects, a battery pack includes a battery pack housing andelectrochemical cells disposed in the housing. The housing comprising acontainer that includes a base, an outer wall, a first inner wall and asecond inner wall. The base includes an inner surface, and outer surfaceopposed to the inner surface, and a peripheral edge that joins the innersurface to the outer surface. The outer wall surrounds the peripheraledge and protrudes from the base in a direction that is normal to theinner surface of the base. The outer wall includes a first portion, asecond portion adjoining the first portion, a third portion adjoiningthe second portion and opposed to the first portion, and a fourthportion opposed to the second portion. The first inner wall extendsbetween the first portion and the third portion, and the first innerwall is fixed to each of the first portion and the third portion. Thesecond inner wall extends between the first portion and the thirdportion, and is disposed between the first inner wall and the fourthportion. The second inner wall is movable relative to the outer wallsuch that a spacing of the second inner wall from the first inner wallcan be changed.

The battery pack may include one or more of the following features: Thefirst inner wall is spaced apart from the second portion and the fourthportion, whereby a gap exists between the first inner wall and thesecond portion. Each of the first inner wall and the second inner wallis hollow and includes opposed inner and outer surfaces and ribs thatextend between the opposed inner and outer surfaces, the ribs definingvacancies within each of the first inner wall and the second inner wall.The second inner wall has an inner surface that is parallel to and facesthe second portion, and an outer surface that faces the fourth portion,and at least a portion of the outer surface of the second inner wall isnot parallel to the fourth portion. A spacer is disposed between thesecond inner wall and the fourth portion. The battery pack includes abattery management device including electronics configured to monitorand control function of the electrochemical cells, and the batterymanagement device is disposed in the container between the second innerwall and the fourth portion. The outer wall is formed of a firstelement, a second element formed separately from, and detachablyconnected to, the first element, and a latching member. The firstelement includes the first portion, the second portion and the thirdportion arranged in a U-shape, and an inner surface of the first elementincludes first surface features configured to receive the latchingmember. The second element includes the fourth portion, and an innersurface of the second element includes second surface featuresconfigured to receive the latching member and cooperate with firstsurface features to detachably connect the first element to the secondelement. The electrochemical cells are arranged side-by-side within thehousing, and an insulating sheet is disposed between eachelectrochemical cell. The electrochemical cells are supported on thebase such that an outer surface of the cell housing directly contactsthe base inner surface.

In some aspects, a battery pack that produces a voltage of less than 60V can be used as part of the power system of a hybrid electric vehicle,whereby it is possible to reduce power system costs and complexity.Because the voltage produced by the battery pack is less than 60 V, thecomponents used to form the battery pack are less expensive.

The battery pack housing is configured to receive a plurality ofprismatic cells. In some embodiments, the prismatic cells have a metalhousing and thus may have an electric charge due to contact between theelectrolyte disposed in the cell and the cell housing. The battery packhousing is formed of a material that is electrically nonconductive andthermally conductive. This can be compared to some conventional batterypack housings which are formed of an electrically conductive materialsuch as metal, and in which insulating structures must be interposedbetween the prismatic cell housing and the battery pack housing, as wellas between adjacent cells. By forming the battery pack housing of anon-electrically conductive material, it is possible for the cells torest in direct contact with the housing without risk of forming anelectrical short circuit. Since the insulating structures can besimplified, the battery pack housing can be reduced in size and the costof materials and assembly can be reduced.

By forming the battery pack housing of a thermally conductive material,passive cooling of the battery pack housing and the cells disposedtherein is enhanced. Advantageously, an outer surface of the batterypack housing includes cooling fins that further facilitate heat exchangewith the ambient air.

The battery pack housing includes a container and a lid that closes anopen end of the container. The container is formed having a dual-wallsidewall structure in which inner wall portions are spaced apart fromthe outer wall. In the illustrated embodiments, the container includestwo inner wall portions disposed inside the outer wall and arranged inparallel to each other and to opposed side portions of the outer wall.The first inner wall portion is fixed within the container so as to beadjacent to and spaced apart from one side portion of the outer wall.The second inner wall portion is moveable within the container and islocated adjacent to and spaced apart from the opposed side portion ofthe outer wall. The electrochemical cells are disposed side-by-side inthe container between the first and second inner wall portions such thata stacking axis that is transverse to the confronting sides of the cellspasses through the one side portion and the opposed portion of the outerwall. During assembly, the second inner wall portion is moved as a unittoward the first inner wall portion placing the cells under acompressive load. In addition, the stacking axis is parallel to a cellgrowth direction of the prismatic cells, whereby any expansion of thecells due to cell growth results in a force applied to the inner wallportions along the stacking axis. The inner wall portions are configuredto accommodate stresses due to prismatic cell growth. For example, uponsufficient growth, the inner wall portions may change shape (deform orslightly deflect) to accommodate the force. Because the inner wallportions are spaced apart from the outer wall portions, and theprismatic cell growth is accommodated by the inner wall portions, theforce is not applied to the outer wall portions. As a result, the outerwall is dimensionally stable. By providing an outer wall that isdimensionally stable, a seal that is provided between the outer wall ofthe container and the lid is more reliable than some battery packhousings in which the sidewall may be affected by cell growth. The sealprevents particles and/or moisture from entering the interior space ofthe battery pack housing, whereby battery pack operability, reliabilityand longevity is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is top perspective view of a battery pack.

FIG. 2 is a top perspective view of the battery pack of FIG. 1 with thelid omitted.

FIG. 3 is a schematic view of the arrangement of electrode and separatorstrips used to form the electrode assembly of each cell.

FIG. 4 is a cross-sectional view of the electrode assembly as seen in adirection transverse to the electrode winding axis.

FIG. 5 is a perspective exploded view of a portion of the cell arrayillustrating the alternating arrangement between cells and insulativeseparator plates within the cell array.

FIG. 6 is a top perspective exploded view of the container of thebattery pack housing.

FIG. 7 is a top plan view of the second element of the container.

FIG. 8 is a cross-sectional view of the container as seen along line 8-8of FIG. 7.

FIG. 9 is a cross-sectional view of the container as seen along line 9-9of FIG. 10.

FIG. 10 is a top plan view of one end of the container of FIG. 6illustrating a battery management device disposed in the container.

FIG. 11 is a top plan view of an alternative embodiment container.

FIG. 12 is a top plan view of one end of the container of FIG. 11illustrating a battery management device disposed in the container.

FIG. 13 is a perspective view of another alternative embodimentcontainer.

DETAILED DESCRIPTION

Referring to FIGS. 1-2, a battery pack 1 is a power generation andstorage device that includes electrochemical cells 2 that areelectrically interconnected and stored in an organized manner within abattery pack housing 40. The battery housing 40 includes a container 60and a lid 50 that closes an open end of the container 60. Within thebattery pack housing 40, the array of cells 2 are electrically connectedin series or in parallel to battery pack terminals 54, 55 that protrudefrom the lid 50. The battery pack housing 40 including the lid 50 andcontainer 60 is formed of a non-electrically conductive material. Inaddition, the container 60 has passive cooling features as well asfeatures that minimize outer wall stress due to electrochemical cellgrowth, as discussed in detail below.

Referring to FIGS. 3-5, the cells 2 are lithium-ion cells that include acell housing 20 that encloses an electrode assembly 4 and an electrolyteto form a power generation and storage unit. The electrode assembly 4includes at least one positive electrode 6, at least one negativeelectrode 8, a first electrically insulative separator 10 disposedbetween the positive and negative electrodes 6, 8, and a secondelectrically insulative separator 12 disposed on the other side of oneof the positive electrode 6 and the negative electrode 8.

The positive and negative electrodes 6, 8 each have a layered structureto facilitate insertion and/or movement of lithium-ions. In theillustrated embodiment, the positive electrode 6 is formed of copperwith a graphite coating, and the negative electrode 8 is formed ofaluminum with a lithiated metal oxide coating. The separators 10, 12 areformed of an electrically insulating material such as a tri-layerpolypropylene-polyethylene-polypropylene membrane.

The electrodes 6, 8 and separators 10, 12 are elongate strips ofmaterial that are stacked and then wound about an elliptically shapedmandrel to form an elliptically-shaped or race track-shaped jelly rollassembly 4. As used herein, the term ‘strip’ refers to a geometry thatincludes a length l_(e) that is large (e.g., on the order of 1000×)relative to the height h_(e), and a height h_(e) that is large (e.g., onthe order of 1000×) relative to the thickness t_(e). For example, insome applications, the electrodes 26, 28 may have a thickness t_(e) of0.03 mm, a height h_(e) of 60 mm and a length l_(e) of 45 m.

The cell housing 20 has a rectangular prism shape (e.g., prismatic), andincludes a first side 22, and a second side 24 opposed to the first side22, a third side 26 adjoining the first side 22 and the second side 24,and a fourth side 28 opposed to the third side 26 and adjoining thefirst side 22 and the second side 24. The first and second sides 22, 24have the same height as the third and fourth sides 26, 28, but have alarger width. For example, in the illustrated embodiment, the width ofthe first and second sides 22, 24 is about twice the height, whereas thewidth of the third and fourth sides 26, 28 is about one-fourth of theheight. In addition, the cell housing 20 includes a first end 30 throughwhich a positive terminal 34 and a negative terminal 36 protrude, and asecond end 32 opposed to the first end. The electrode assembly 4 isdisposed in the cell housing 20 such that the winding axis (e.g., theaxis about which the electrodes and separators are wound) 14 extendsthrough the first and second ends 30, 32.

The electrode assembly 4 experiences dimensional changes during batterycharge and discharge. This is due at least in part to expansion of thelayered structure of the positive and negative electrodes in theelectrode thickness direction due to expansion of the active materialsduring cycling. The expansion of the jelly roll electrode assembly 4within the cell housing 20 results in “cell growth”, which correspondsto the outward bowing of the first and second sides 22, 24 of the cellhousing 20 in a direction transverse to the winding axis and normal toan outer surface of the first and second sides 22, 24. The battery packhousing includes features which accommodate the growth of the cells 2disposed therein, as discussed further below.

Referring to FIGS. 2 and 5, the array of cells 2 is disposed in thecontainer 60 of the battery pack housing 40. For example, in theillustrated embodiment, the array includes a single row of twelve cellsarranged side-by-side such that the second side 24 a of one cell 2 afaces the first side 22 b of the adjacent cell 2 b, and such that thefirst end 30 of each cell faces the lid 50. A stacking axis 16corresponding to the stacking direction of the cell array is transverseto the facing surfaces (e.g., the first and second sides 22, 24) of thecells 2. An insulating separator plate 18 is disposed between facingsurfaces of adjacent cells 2. The array is arranged within the batterypack housing 40 such that the first side 22 of an outermost cell 2 (1)at one end of the array faces and abuts a first inner wall 101 of thecontainer 60, and the second side 24 of an outermost cell 2(12) at theopposed end of the array faces and abuts a second inner wall 121 of thecontainer 60.

Referring to FIGS. 2 and 6, the container 60 is a box-like structurethat includes a base 61, an outer wall 70 that surrounds the base 61 andinner walls 101, 121 disposed between portions of the outer wall 70 andthe cells 2. The base 61 is rectangular, and has a length dimension thatis greater than its width dimension. The base 61 includes an innersurface 62 and an outer surface 63 opposed the inner surface 62. Theouter wall 70 surrounds a peripheral edge of the base 61 and protrudesfrom the base 61 in a direction that is normal to the base inner surface62.

The outer wall 70 forms a rectangular closed section when seen in topplan view, and thus includes four orthogonal outer wall portions. Inparticular, the outer wall 70 includes a first portion 71 that extendsalong the length of the base 61, a second portion 72 adjoining the firstportion 71 and extending a long the width of the base 61. The outer wall70 includes a third portion 73 that adjoins the second portion 72 and isopposed to the first portion 71, and a fourth portion 74 that is opposedto the second portion 72 and adjoins the first portion 71 and the thirdportion 73. The first and third portions 71, 73 have a larger area thanthe second and fourth portions 72, 74, and are parallel to the stackingaxis 16 of the cells 2. The outer surface 76 of the outer wall 70includes surface features that enhance cooling of the battery pack. Inparticular, the outer surface of the first and third portions 71, 73includes outwardly protruding cooling ribs 78. The cooling ribs 78extend between the base 61 and a free edge 79 of the outer wall 70, andcover an area that corresponds to the position of the cells 2 disposedwithin the battery pack 1.

The first inner wall 101 is disposed inside the outer wall 70, andextends in the width direction. More specifically, the first inner wall101 is parallel to and spaced apart from both the second portion 72 andthe fourth portion 74, and is disposed between a center 64 of thecontainer 60 and the second portion 72 such that a first gap g₁ existsbetween the first inner wall 101 and the second portion 72. The firstgap g₁ is small relative to an overall length l_(o) of the container 60as measured between outer surfaces of the second portion 72 and thefourth portion 74, as well as the dimension d of a cell 2 in thestacking direction. For example, in some embodiments, the first gap g₁is in a range of 0.5 percent to 2.0 percent of the overall length l_(o).Similarly, in some embodiments, the first gap g₁ is in a range of 5percent to 30 percent of the dimension d of the cell 2 in the stackingdirection.

The first inner wall 101 includes a pair of parallel, spaced-apartplates 102, 103 that are parallel to the second portion 72 and thefourth portion 74. Angled ribs 106 extend between inner surfaces of theplates 102, 103, resulting in vacancies 107 being formed within thefirst inner wall 101 that contribute to the ability of the first innerwall 101 to deform under loads applied in a direction normal to thesurfaces of the plates 102, 103, such as occurs during cell growth.

The first inner wall 101 extends between the first portion 71 and thethird portion 73. In particular, the first inner wall 101 abuts and isfixed to each of the first portion 71, the base 61 and the third portion73. For example, in some embodiments, the inner wall 101 is formedintegrally with outer wall 70 and the base 61. In other embodiments, theinner wall 101 is fixed to the outer wall 70 and the base 61 duringmanufacture.

The second inner wall 121 is disposed inside the outer wall 70, andextends in the width direction. The second inner wall 121 is parallel toand spaced apart from the second portion 72 and the fourth portion 74.In addition, the second inner wall 121 is disposed between the center 64of the container 60 and the fourth portion 74 so as to reside betweenthe first inner wall 101 and the fourth portion 74. A second gap g₂exists between the second inner wall 121 and the fourth portion 74. Thesecond gap g₂ is small relative to the overall length l_(o) of the firstportion 71, and is larger than the dimension d of a cell 2 in thestacking direction. For example, in some embodiments, the second gap g₂is in a range of 10 percent to 20 percent of the overall length l_(o).However, in some embodiments, the second gap g₂ is in a range of 100percent to 300 percent of the dimension d of the cell 2 in the stackingdirection.

Like the first inner wall 101, the second inner wall 121 includes a pairof parallel, spaced-apart plates 122, 123 that are parallel to thefourth portion 74. Angled structural ribs 126 extend between innersurfaces of the plates 122, 123, resulting in vacancies 127 being formedwithin the second inner wall 121 that contribute to the ability secondinner wall 121 to deform under loads applied in a direction normal tothe surfaces of the plates 122, 123, such as occurs during cell growth.

Referring to FIGS. 6-8, the second inner wall 121 extends between thefirst portion 71 and the third portion 73, but is not fixed thereto.Instead, the second inner wall 121 is fixed to the fourth portion 74 viaa two pair of arms 132, 142 that extend inward from an inner surface ofthe fourth portion 74 and serve as a rigid spacer structure thatmaintains the gap g2 between the second inner wall 121 and the fourthportion 74. The first pair of arms 132 is provided along one side edgeof the fourth portion 74 so as to be adjacent the first portion 71, andthe second pair of arms 142 is provided along the opposed side edge ofthe fourth portion 74 so as to be adjacent the third portion 73. A firstcatch plate 88 is disposed between the arms 133, 134 of the first pairof arms 132, and a second catch plate 89 is disposed between the arms143, 144 of the second pair of arms 142. The first and second catchplates 88, 89 are parallel to the base 61 and have a catch plate opening88 a, 89 a that is disposed between the second inner wall 121 and thefourth portion 74. The catch plates 88, 89 are part of a latchingstructure used to retain the fourth portion 74 in an assembledconfiguration with the remainder of the outer wall 70, as discussedfurther below.

In the embodiment illustrated in FIGS. 1-8, the outer wall 70 is formedas two, separate elements 66, 68 that are configured to detachablyengage with each other to form the rectangular closed section describedabove. The first element 66 of the outer wall 70 includes the first,second and third portions 71, 72, 73 that are formed integrally with thebase 61 and arranged in a U-shaped configuration when seen in top planview. The second element 68 of the outer wall 70 includes the fourthportion 74, which, when assembled with the first element 66, closes theopen end 90 of the U-shaped first element 66 (referred to hereafter asthe U open end 90). The second element 68, corresponding to fourthportion 74, is formed separately from, and detachably connected to, thefirst element 66 via the latching structure.

The latching structure is provided on the inner surface 75 of the outerwall 70, and includes a first pair of eyes 80, 81 that protrude from aninner surface of the first portion 71 at a location adjacent the U openend 90. The eyes 80, 81 of the first pair include openings 80 a, 81 athat are aligned along a first axis 86 that is normal to the base innersurface 62. The latching structure includes a second pair of eyes 82, 83(eye 83 is not visible) that protrude from an inner surface of the thirdportion 73 at a location adjacent the U open end 90. The eyes 82, 83 ofthe second pair include openings 82 a, 83 a that are aligned along asecond axis 88 that is normal to the base inner surface 62. The latchingstructure also includes the first catch plate 88 that protrudes from theinner surface of the fourth portion 74 at a location adjacent the firstportion 71, and the second catch plate 89 that protrudes from an innersurface of the fourth portion 74 at a location adjacent the thirdportion 73. When the second element 68, or fourth portion 74, isassembled with the first element 66, the first catch plate 88 isinterposed between the eyes 80, 81 of the first pair such that the firstcatch plate opening 88 a is aligned along the first axis 86 with theopenings 80 a, 81 a of the first pair of eyes. In addition, the secondcatch plate 89 is interposed between the eyes 82, 83 of the second pairsuch that the second catch plate opening 89 a is aligned along thesecond axis 87 with the openings 82 a, 83 a of the second pair of eyes.The latching structure includes a first pin 84 that is aligned with thefirst axis 86 and passes through the openings 80 a, 88 a, 81 a of thefirst pair of eyes and the first catch plate 88, and a second pin 85that is aligned with the second axis 87 and passes through the openings82 a, 89 a, 83 a of the second pair of eyes and the second catch plate89. In particular, the first and second pins 84, 85 cooperate withcorresponding eyes and catch plates formed on the outer wall innersurface 75 to detachably connect the first element 66 to the secondelement 68.

Referring to FIGS. 1 and 9, the lid 50 of the battery pack housing 40 isshaped and dimensioned to close the open end of the container 60. Aperiphery of the container-facing surface 52 of the lid 50 includesopenings (not shown) that receive and engage with upright latches 77provided on the container outer wall 70. The openings and the uprightlatches cooperate to retain the lid 50 in a closed configuration withrespect to the container open end. The positive terminal 54 and anegative terminal 55 protrude from an outward-facing surface 51 of thelid 50.

The battery pack housing 60 is formed of a material that is electricallynonconductive and thermally conductive. For example, the battery packhousing 60 may be formed of a molded, high strength plastic withadditives that improve thermal conductivity and provide electricalisolation. When used in conjunction with the cooling ribs 78, thethermally conductive battery pack housing 60 provides passive cooling ofthe cells 2 during operation, whereby cell operating efficiency isimproved and damage to heat sensitive components of the cell 2 isprevented.

A seal 56 is provided between a periphery of the container-facingsurface 52 of the lid 50 and the free edge 79 of the container outerwall 70. The seal may be a gasket or a sealing adhesive or achieved byother conventional techniques. In some embodiments where a sealingadhesive is used, the sealing adhesive permits removal of the lid 50from the container 60, while in other embodiments the sealing adhesiveprovides a permanent bonding of the lid 50 to the container 60.

Referring to FIGS. 6, 7 and 10, the second element 68 includes thesecond inner wall 121 that is parallel to and spaced apart from thefourth portion 74 via the two pair of arms 132, 142. The gap g₂ betweenthe second inner wall 121 and the fourth portion 74 is used to receive abattery management device 53. The battery management device 53 iselectrically connected to each cell 2 disposed in the battery packhousing 40, and includes electronics configured to monitor and controlfunction of the electrochemical cells. For example, the batterymanagement device 53 may regulate the battery pack 1 by activelyinfluencing the electric current flow. The electronics may include aprinted circuit board, a resistance busbar, a relay, a fuse, etc. Insome embodiments, the battery management device 53 is incorporated intothe lid structure, and protrudes from the lid container-facing surface52 and into the vacancy between the second inner wall 121 and the fourthportion of the outer wall 70. In other embodiments, the batterymanagement device 53 is provided separately from the lid 50, and isdisposed within the vacancy between the second inner wall 121 and thefourth portion of the outer wall 70.

The battery pack 1 is assembled as follows. The first element 66 isseparated from the second element 68, and cells 2 are placed within thefirst element 66 while the second element 68 is disengaged from thefirst element 66. The cells 2 are arranged side-by-side in a 1×(numberof cells) array with the electrically-insulating separator plates 18disposed in between adjacent cells 2. The number of cells 2 placedwithin the battery pack 1 and the dimensions of cells 2 are set so thatthe overall length of the cell array in the stacking direction isgreater than the distance d2 between facing surfaces of the first andsecond inner walls 101, 121. The second element 68 is partiallyassembled with the first element 66 with the second inner wall 121abutting the outermost cell 2(12) of the cell array. In this initialposition, the fourth portion 74 does not abut the first and thirdportions 71, 73 due to the overall length of the cell array. The secondelement 68 including the second inner wall 121 is then pushed toward thefirst inner wall 101 until the fourth portion 74 abuts the first andthird portions 71, 73. In this abutting position, the openings 80 a, 81a, 82 a, 83 a, 88 a, 89 a of the latching structure are aligned alongthe corresponding axes 86, 87. At this time, the pins 84, 85 areinserted through the corresponding openings, whereby the second element68 is secured to the first element 66 and the container is complete, andwhereby the cells 2 are disposed within the container 60 undercompression in the direction of the stacking axis 16. In someembodiments, a second seal (not shown) may be provided between abuttingsurfaces of the first element 66 and the second element 68. This methodof assembly is achievable since the second element 68 including thesecond inner wall 121 is movable relative to the first element 66including the first portion 71, the base 61 and the third portion 73. Asused herein, the term “movable” refers to movement of the second innerwall 121 as a unit relative to the first and third portions 71, 73, andis considered to be different than the terms “deformation” and“deflection” which are used to refer to changes in the shape of thefirst and second inner walls 101, 121.

Referring to FIGS. 11-12, an alternative embodiment container 260 may beused with the lid 50 to form a battery pack. The container 260 issimilar to the container 60 described above with respect to FIGS. 1-10,and common elements will be referred to using common reference numbers.The container 260 is a box-like structure that includes the base 61, anouter wall 270 that surrounds the base 61 and inner walls 101, 221disposed between portions of the outer wall 270 and the cells 2. Theouter wall 270 and the second inner wall 221 of the container 260 differfrom the previously-described outer wall 70 and second inner wall 121,as now described.

In the container 260, the outer wall 270 and the base 61 are a unitarystructure that includes four orthogonal outer wall portions 271, 272,273, 274 that together surround a peripheral edge of the base 61 andprotrude from the base 61 in a direction that is normal to the baseinner surface 62. In some embodiments, the outer wall portions 271, 272,273, 274 are formed integrally (e.g., as a monolithic structure) witheach other and the base 61 for example using a molding process. In otherembodiments, the outer wall portions 271, 272, 273, 274 are fixed toeach other and the base 61 during manufacture.

As in the previously-described embodiment, the second inner wall 221 isdisposed inside the outer wall 270, and extends in the width direction.The second inner wall 221 is parallel to and spaced apart from thesecond portion 272 and the fourth portion 274. In addition, the secondinner wall 221 is disposed between the first inner wall 101 and thefourth portion 274.

The second inner wall 221 includes the pair of parallel, spaced-apartplates 122, 123 that are parallel to the fourth portion 274. Angledstructural ribs 126 extend between inner surfaces of the plates 122,123, resulting in vacancies 127 being formed within the second innerwall 221 that contribute to the ability of the second inner wall 221 todeform under loads applied in a direction normal to the surfaces of theplates 122, 123, such as occurs during cell growth.

The second inner wall 221 extends between the first portion 271 and thethird portion 273, but is not fixed to the outer wall 270 or the base61. As a result, the second inner wall 221 is movable relative to theouter wall 170 such that a spacing of the second inner wall 221 fromboth the first inner wall 101 and the fourth portion 274 can be changed.For example, the second inner wall 221 is free-floating with respect tothe outer wall 270 and the base 61. Since the second inner wall 221 isfree-floating, assembly of the cells 2 within the container 260 under acompression load in the stacking direction can be accomplished whileproviding a unitary, four-sided outer wall structure. The unitary,four-sided outer wall structure is dimensionally stable due to itsunitary structure in combination with use of the inner walls 101, 221,and thus can be reliably sealed.

When the battery pack 100 is assembled, the second inner wall 221 isdisposed between the array of cells 2 and the fourth portion 274 suchthat the second gap g₂ exists between the second inner wall 221 and thefourth portion 274. The gap g₂ is achieved by providing first and secondspacers 232, 242 between the second inner wall 221 and the fourthportion 274. The first spacer 232 is provided along one side edge of thefourth portion 274 so as to be adjacent the first portion 271, and thesecond spacer 242 is provided along the opposed side edge of the fourthportion 274 so as to be adjacent the third portion 273. In theillustrated embodiment, the first and second spacers 232, 242 arerectangular tubes that are dimensioned to provide the desired gap g₂. Insome embodiments, the first and second spacers 232, 242 are taperedalong an axis that is normal to the base inner surface 62, whereby thefirst and second spacers 232, 242 are used drive the second inner wall221 and the cell array toward the first inner wall 101 during assembly,and thus apply a compressive force to the cell array in the stackingdirection. In addition, the first and second spacers 232, 242 maintainthe gap g₂ between the second inner wall 221 and the fourth portion 274upon assembly.

Referring to FIG. 13, another alternative embodiment container 360 maybe used with the lid 50 to form a battery pack. The container 360 issimilar to the container 260 described above with respect to FIGS.11-12, and common elements will be referred to using common referencenumbers. The container 360 is a box-like structure that includes thebase 61, an outer wall 270 that surrounds the base 61 and inner walls101, 321 disposed between portions of the outer wall 270 and the cells2. The second inner wall 321 of the container 360 differs from thesecond inner wall 221 of FIGS. 11-12 as described in detail below.

In the container 360, the outer wall 270 and the base 61 are a unitarystructure that includes four orthogonal outer wall portions 271, 272,273, 274 that together surround a peripheral edge of the base 61 andprotrude from the base 61 in a direction that is normal to the baseinner surface 62. In some embodiments, the outer wall portions 271, 272,273, 274 are formed integrally (e.g., as a monolithic structure) witheach other and the base 61 for example using a molding process. In otherembodiments, the outer wall portions 271, 272, 273, 274 are fixed toeach other and the base 61 during manufacture.

As in the previously-described embodiment, the second inner wall 321 isdisposed inside the outer wall 270, and extends in the width direction.The second inner wall 321 is parallel to and spaced apart from thesecond portion 272 and the fourth portion 274. In addition, the secondinner wall 321 is disposed between the first inner wall 101 and thefourth portion 274.

The second inner wall 321 is formed having an open cell structureincluding angled structural ribs 326 that extend in a directionperpendicular to the second inner wall inner face 322, in parallel tothe first and third outer wall portions 271, 273, and define rectangularopen cells or vacancies 327. The vacancies 327 formed within the secondinner wall 321 contribute to the ability of the second inner wall 321 todeform under loads applied in a direction normal to the second innerwall 321, such as occurs during cell growth. Although the second innerwall inner face 322 is parallel to the second and fourth portions 272,274, the opposed second inner wall outer face 323 may not be parallel tothe second and fourth portions 272, 274 in order to provide a wallgeometry in which wall strength is optimized. The illustrated embodimentshows one possible second inner wall 321 configuration, in which theouter face 323 is curved as seen in a top plan view of the container360. In this example, the second inner wall outer face 323 is convex soas to protrude toward the second portion, whereby a center portion ofthe second inner wall 321 has a greater thickness than portions of thesecond inner wall 321 adjacent the first and third portions 271, 273.

The second inner wall 321 extends between the first portion 271 and thethird portion 273, but is not fixed to the outer wall 270 or the base61. As a result, the second inner wall 321 is movable relative to theouter wall 270 such that a spacing of the second inner wall 321 fromboth the first inner wall 101 and the fourth portion 274 can be changed.For example, the second inner wall 321 is free-floating with respect tothe outer wall 270 and the base 61. Since the second inner wall 321 isfree-floating, assembly of the cells 2 within the container 260 under acompression load in the stacking direction can be accomplished whileproviding a unitary, four-sided outer wall structure. The unitary,four-sided outer wall structure is dimensionally stable due to itsunitary structure in combination with use of the inner walls 101, 321,and thus can be reliably sealed.

When the battery pack 100 is assembled, the second inner wall 321 isdisposed between the array of cells 2 and the fourth portion 274 suchthat the second gap g₂ exists between the second inner wall 321 and thefourth portion 274. The gap g₂ is achieved by providing first and secondspacers 332, 342 between the second inner wall 321 and the fourthportion 274. The first spacer 332 is provided along one side edge of thefourth portion 274 so as to be adjacent the first portion 271, and thesecond spacer 342 is provided along the opposed side edge of the fourthportion 274 so as to be adjacent the third portion 273. In theillustrated embodiment, the first and second spacers 332, 342 are rigidelements that are dimensioned to provide the desired gap g₂, and areshaped to correspond to, and cooperate with, the shape of the secondinner wall outer face 323. In particular, the shape of the first andsecond spacers 332, 342 is optimized together with the shape of thesecond inner wall 321 to provide optimal strength of the second innerwall 321. In some embodiments, the first and second spacers 332, 342 maybe tapered along an axis that is normal to the base inner surface 62,whereby the first and second spacers 332, 342 are used drive the secondinner wall 321 and the cell array toward the first inner wall 101 duringassembly, and thus apply a compressive force to the cell array in thestacking direction. In addition, the first and second spacers 332, 342maintain the gap g₂ between the second inner wall 321 and the fourthportion 274 upon assembly.

Although the containers 60, 260, 360 described herein each include afixed first inner wall 101 that is separated from the outer wall 70, 270via a first gap g₁, it is contemplated that the gap g₁ may be eliminatedin some embodiments, whereby the inner wall 101 would become the secondportion 72, 272 of the outer wall 70, 720, and would have propertiesthat would permit some deformation of the inward facing surface 122thereof.

Although the cells 2 are described as housing the electrode assembly 4having a jelly roll electrode configuration, the electrode assembly 4 isnot limited to this electrode configuration. For example, the electrodeassembly 4 may include a stacked or folded arrangement of electrodeplates, or other suitable electrode arrangement.

Although the cells 2 are described as being lithium ion cells, the cells2 are not limited to this type of cell. For example, the cells 2 mayinclude different combinations of electrode materials and electrolytes,including lead-acid, nickel cadmium (NiCd), nickel metal hydride (NiMH),and lithium ion polymer.

Although the illustrated embodiment includes twelve cells 2 in the cellarray, the battery pack 1 is not limited to having twelve cells 2. Thenumber of cells used may be greater or fewer than twelve, and isdetermined by the requirements of the specific application.

Selective illustrative embodiments of the battery pack and battery packhousing are described above in some detail. It should be understood thatonly structures considered necessary for clarifying these devices havebeen described herein. Other conventional structures, and those ofancillary and auxiliary components of the battery pack system, areassumed to be known and understood by those skilled in the art.Moreover, while working examples of the battery pack and battery packhousing been described above, the battery pack and/or battery packhousing is not limited to the working examples described above, butvarious design alterations may be carried out without departing from thedevices as set forth in the claims.

What is claimed is:
 1. A battery pack housing configured to receive aplurality of electrochemical cells, the battery pack housing comprisinga container that includes a base that includes an inner surface, anouter surface opposed to the inner surface, and a peripheral edge thatjoins the inner surface to the outer surface, an outer wall thatsurrounds the peripheral edge and protrudes from the base in a directionthat is normal to the inner surface of the base, the outer wallincluding a first portion, a second portion adjoining the first portion,a third portion adjoining the second portion and opposed to the firstportion, and a fourth portion opposed to the second portion, a firstinner wall that extends between the first portion and the third portion,the first inner wall being fixed to each of the first portion and thethird portion, and a second inner wall that extends between the firstportion and the third portion, is disposed between the first inner walland the fourth portion, the second inner wall being movable relative tothe outer wall such that a spacing of the second inner wall from thefirst inner wall can be changed.
 2. The battery pack housing of claim 1,wherein the first inner wall is spaced apart from the second portion andthe fourth portion, whereby a gap exists between the first inner walland the second portion.
 3. The battery pack housing of claim 1, whereineach of the first inner wall and the second inner wall is hollow andincludes opposed inner and outer surfaces and ribs that extend betweenthe opposed inner and outer surfaces, the ribs defining vacancies withineach of the first inner wall and the second inner wall.
 4. The batterypack housing of claim 1, wherein a spacer is disposed between the secondinner wall and the fourth portion.
 5. The battery pack housing of claim1, wherein the second inner wall has an inner surface that is parallelto and faces the second portion, and an outer surface that faces thefourth portion, and at least a portion of the outer surface of thesecond inner wall is not parallel to the fourth portion.
 6. The batterypack housing of claim 1, wherein a portion of an outer surface of theouter wall is formed having outwardly protruding cooling ribs.
 7. Thebattery pack housing of claim 1, wherein the battery pack housing isformed of a non-electrically conductive material.
 8. The battery packhousing of claim 1, wherein the outer wall is formed of a first element,a second element formed separately from, and detachably connected to,the first element, and a latching member, wherein the first elementincludes the first portion, the second portion and the third portionarranged in a U-shape, an inner surface of the first element includingfirst surface features configured to receive the latching member, thesecond element includes the fourth portion, and an inner surface of thesecond element includes second surface features configured to receivethe latching member and cooperate with first surface features todetachably connect the first element to the second element.
 9. Thebattery pack housing of claim 8, wherein the second element includes thesecond inner wall, and the second inner wall is parallel to and spacedapart from the fourth portion via a spacer.
 10. The battery pack housingof claim 8, wherein the latching member is a pin, wherein the firstsurface features include a first through opening and the second surfacefeatures include a second through opening, and the pin extends throughboth the first through opening and the second through opening.
 11. Thebattery pack housing of claim 10, wherein the second through opening isaligned with the first through opening along an axis normal to the innersurface of the base.
 12. A battery pack comprising a battery packhousing and electrochemical cells disposed in the housing, the housingcomprising a container that includes a base that includes an innersurface, an outer surface opposed to the inner surface, and a peripheraledge that joins the inner surface to the outer surface, an outer wallthat surrounds the peripheral edge and protrudes from the base in adirection that is normal to the inner surface of the base, the outerwall including a first portion, a second portion adjoining the firstportion, a third portion adjoining the second portion and opposed to thefirst portion, and a fourth portion opposed to the second portion, afirst inner wall that extends between the first portion and the thirdportion, the first inner wall being fixed to each of the first portionand the third portion, and a second inner wall that extends between thefirst portion and the third portion, is disposed between the first innerwall and the fourth portion, the second inner wall being movablerelative to the outer wall such that a spacing of the second inner wallfrom the first inner wall can be changed.
 13. The battery pack of claim12, wherein the first inner wall is spaced apart from the second portionand the fourth portion, whereby a gap exists between the first innerwall and the second portion.
 14. The battery pack of claim 12, whereineach of the first inner wall and the second inner wall is hollow andincludes opposed inner and outer surfaces and ribs that extend betweenthe opposed inner and outer surfaces, the ribs defining vacancies withineach of the first inner wall and the second inner wall.
 15. The batterypack of claim 12, wherein the second inner wall has an inner surfacethat is parallel to and faces the second portion, and an outer surfacethat faces the fourth portion, and at least a portion of the outersurface of the second inner wall is not parallel to the fourth portion.16. The battery pack of claim 12, wherein a spacer is disposed betweenthe second inner wall and the fourth portion.
 17. The battery pack ofclaim 12, comprising a battery management device including electronicsconfigured to monitor and control function of the electrochemical cells,the battery management device disposed in the container between thesecond inner wall and the fourth portion.
 18. The battery pack of claim12, wherein the outer wall is formed of a first element, a secondelement formed separately from, and detachably connected to, the firstelement, and a latching member, wherein the first element includes thefirst portion, the second portion and the third portion arranged in aU-shape, an inner surface of the first element including first surfacefeatures configured to receive the latching member, the second elementincludes the fourth portion, an inner surface of the second elementincludes second surface features configured to receive the latchingmember and cooperate with first surface features to detachably connectthe first element to the second element.
 19. The battery pack of claim12, wherein the electrochemical cells are arranged side-by-side withinthe housing, and an insulating sheet is disposed between eachelectrochemical cell.
 20. The battery pack of claim 12, wherein theelectrochemical cells are supported on the base such that an outersurface of the cell housing directly contacts the base inner surface.